Been working on this duplicate tool quite a bit. Been sending the author screen shots of errors and bugs I have found. The first release seemed to only work on certain host providers as I am doing shared hosting for over 200+ wp blogs.
He just released version 1.1 and it seems to work really GREAT!
For my position, I manage over 200+ word press blogs (English, French, and Spanish) and having duplicate content on posts for us is a big NO-NO. (think google panada)
I would highly recommend this plug-in as I know the author is continually trying to make the plug in better, and responds to questions.